Conventionally, a light system of a projection apparatus is usually provided with a color wheel. When a beam in a specific wavelength is emitted by a light source and projects to the color wheel, the beam in the specific wavelength is converted into a beam in the required wavelength via a wavelength conversion material coated on a single segment or plural segments of the color wheel. Consequently, the converted beam is outputted. Through the combinations of the outputted beams and the colors, a multicolor image can be projected and displayed.
Generally, the color wheel includes single segment or plural segments, and a motor drives the color wheel to rotate. Consequently, the beam in the specific wavelength is converted into one or more single color beam (i.e. in specific wavelength) or multicolor beam (i.e. in specific wavelength region) via the color wheel, and the converted beam is outputted. In order to obtain the relationship between the colors and timing of the outputted beam after the input beam is converted through the color wheel, a mark is usually disposed on the color wheel, and a rotation speed detector is disposed adjacent to the mark correspondingly. When the color wheel is rotated, the rotating speed of the color wheel can be obtained according to the signal variations relative to the mark and the rotation speed detector.
However, the conventional detecting method for detecting the rotating speed of the color wheel by adding the mark to the color wheel is complicated. When the mark is dropped or shifted from the color wheel, the rotation speed detector fails to detect the rotating speed of the color wheel. Besides, when the motor is operated and the wavelength conversion operation is performed by the color wheel, the motor and the color wheel are suffered from high temperature. Consequently, the rotation speed detector disposed adjacent to the motor and the color wheel is burned easily due to the high temperature.
Therefore, there is a need of providing a color wheel rotation speed detecting module in order to overcome the above drawbacks encountered by the prior arts.